What is the minimum number of valves required at the top of an engine with a four stroke cycle?

What is the minimum number of valves required at the top of an engine with a four stroke cycle?

• A. One
• B. Two
• C. Three
• D. Four

Answer: (B)

Four-stroke operation requires both an intake path for the air-fuel mixture and an exhaust path to remove burnt gases. At the top of the engine, you need separate valves to provide those two paths, one opening for intake and one for exhaust. If there were only a single valve, the cylinder couldn’t breathe properly through all four strokes, so the engine wouldn’t run efficiently. Therefore, the smallest valve arrangement that supports a four-stroke cycle is two valves per cylinder: one intake and one exhaust.

Four-stroke operation requires both an intake path for the air-fuel mixture and an exhaust path to remove burnt gases. At the top of the engine, you need separate valves to provide those two paths, one opening for intake and one for exhaust. If there were only a single valve, the cylinder couldn’t breathe properly through all four strokes, so the engine wouldn’t run efficiently. Therefore, the smallest valve arrangement that supports a four-stroke cycle is two valves per cylinder: one intake and one exhaust.